JP2014225873A - Method for building virtual user plane cell, computer system, device for radio communication system, control plane base station, and radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for building a virtual user plane cell including a user plane base station in a radio communication system.SOLUTION: A radio communication system comprises a control plane base station having a coverage area including a plurality of user plane base stations. A method for building a virtual user plane cell including a user plane base station includes the steps of: identifying an anchor user in a coverage area of a control plane base station (step 206); selecting a user plane base station which can offer a service to the anchor user from a plurality of user plane base stations in the coverage area of the control plane base station (step 208); associating a mobile station which can receive the service offer from the selected user plane base station in a user set with the selected user plane base station (step 214); and building a virtual user plane cell including the selected user plane base station and the user associated with the selected user plane base station.

Description

  The present invention relates to the field of wireless communication networks, and in particular, to the field of wireless communication systems having control / user-plane separated networks. Embodiments described herein relate generally to a technique for constructing a virtual user plane cell including a user plane base station in a wireless communication system including a control plane base station having a coverage area including a plurality of user plane base stations. .

  For example, in a wireless communication network having a heterogeneous network, such as a radio access network, control signals and user data signals may be separated into two different networks of overlay type. These networks are so-called networks in which the control plane and user plane are separated (control / user-plane separated networks), that is, networks in which the C plane and U plane are separated (C / U-plane separated networks). .

FIG. 1 shows the overall structure of a network in which the C plane and U plane are separated. The network in which the C plane and the U plane are separated includes an umbrella network (UNW) including one or more control plane base stations (C plane BS). FIG. 1 shows a single control plane base station or C-plane BS100. The C-plane BS 100 can be a macro cell or micro cell base station. FIG. 1 shows a structure in which the C-plane BS 100 is a macro cell base station. These cells operate in current existing frequency bands, eg, 2 GHz frequency bands, using already standardized systems such as LTE or LTE-A, and are used in older mobile stations (MS) That is, backward compatibility is guaranteed for a mobile station that supports only the current standard. The C plane BS100 has a coverage area 102 also called a C plane. The network in which the C plane and the U plane are separated further includes a detached cell network (DCN) including a plurality of user plane base stations, that is, U plane BSs 104 _{1 to} 104 ₅ . . Each base station has a respective coverage area 106 ₁ -106 ₅ defining a user cell or U cell associated with it. A cell formed by the U-plane BS, such as the U-cell 106, is called a small cell. The U cells 106 _{1 to} 106 ₅ form a U plane, that is, a user plane 108 of a network in which the C plane and the U plane are separated. The U cells 106 _{1 to} 106 ₅ are smaller than the coverage area 102 of the macro cell. The DCN includes several U-plane BSs 104 _{1 to} 104 ₅ . This U-plane BS is a smaller cell or U cell 106 _{1 to} 106 ₅ that can operate in a frequency band different from that used in the macro cell or umbrella network, for example, a higher frequency band such as 3 to 5 GHz. Is forming. The U cells 106 _{1 to} 106 ₅ are connected to the umbrella network through respective backhaul links 110 _{1 to} 110 ₅ . FIG. 1 receives a control signal from the macrocell 100 as indicated by arrow 114, and through one of the U cells as indicated by arrow 116, the user data signal through the U-plane BS in the example of FIG. Further shown is a mobile station 112 that communicates.

  A mobile station (MS) connects to the network shown in FIG. 1 using one of several modes, for example using legacy mode or detached cell (DC) mode. be able to. In legacy mode, the umbrella network handles transmission of both control signals and user data signals (C + U transmission). This mode is used to support older MSs or to support a small number of newer MSs that have very high mobility or have low data rate requirements. In this mode, a network of isolated cells is not used. In the DC mode, the umbrella network plays a role of C-plane communication, that is, transmission of control signals (C transmission), and a network of separated cells plays a role of U-plane communication, that is, transmission of user data signals (U transmission). . The U-plane BS is switched on only when necessary. Older mobile stations do not support this mode, so they connect to the network only in legacy mode.

  The problem with the network shown in FIG. 1 is that if some form of interference control is not performed in the U-plane, the interference can have a serious impact on the achievable system capacity. Moreover, sudden traffic fluctuations and network dynamics can severely load parts of the network. As a result, the quality of service (QoS) for the user is degraded in that part of the network, while resources may not be used in other parts of the network.

  Conventional approaches for reducing interference in small cell deployments can be divided into two categories. The first category focuses on orthogonality in terms of time or frequency when transmitting macro and small cells. This is done by defining resource units that are allowed to transmit only in the case of a macro base station (eg, C-plane BS 100 in FIG. 1) or only in the case of a small cell base station (U-plane BS 104 in FIG. 1). . One example is the ABS (almost blank subframe) -eICIC method as defined in the LTE-Advanced standard described in the art with further modifications. Although this approach somehow reduces the interference between the macrocell and the small cell, some resources remain unused, thus reducing the interference at the expense of network capacity. Furthermore, allocating resources in this manner quasi-statically prevents the network from adapting to user distribution and traffic changes within the network. Most importantly, this strategy does not address the interference that occurs between small cells.

The second category for interference mitigation focuses on the autonomous and decentralized operation of small cells that allow them to dynamically adapt to their environment. According to this method, in order to reduce interference and improve capacity, the small cell base station detects its environment and adjusts the usage of resources such as frequency or power. This technique is illustrated in FIG. 2 based on a plurality of small cell base stations that adjust their frequency usage at different times. FIG. 2A shows a U plane 108 having _four U cells 106 _{1 to} 106 4 defined by each U plane BS 104 _{1 to} 104 ₄ . A C-plane BS100 is also shown. At the first time point i, the U-plane BS adjusts the frequency used by the U-plane BS so that it operates at a frequency different from that of the adjacent U-cell. In FIG. 2 (a), U-cells 106 ₁ and 106 ₄ have a sufficiently long distance from each other that they are not expected to interfere even when these two cells use the same frequency, Can operate at the same frequency. In FIG. 2 (b) showing the U plane 108 at time j after time i, at a _second time, a frequency different from the frequency used by the _two U cells 106 ₁ and 106 ₂ at time i is selected. In use, the situation of interference for these two U cells will change somewhat. The drawback with this approach is that it tends to optimize only the local performance of the small cell, and because it lacks wide area information in the small cell, it cannot necessarily optimize the performance of the coverage area 108 of the macrocell as a whole. It is. Furthermore, autonomous and dynamic adjustments limit the ability of the network to react quickly to sudden traffic changes and / or user mobility within the network.

  Several approaches that deal with small cell deployments and techniques that teach transmission power control for communication between base stations and user terminals are already known. According to another method, the cell can dynamically change its size by changing the transmission power level of the control signal based on the measurement value received from the user terminal. However, these approaches focus on allowing the base station to autonomously change the transmit power used for control signals based on measurement reports from users.

  Japanese Patent Application Laid-Open No. 2004-133830 describes that when the power received by the farthest user equipment is out of a predetermined operating band, the user equipment reduces the level of transmission power of the control signal to the small cell base station. Describes a method for sending messages. This technique dynamically adjusts the cell footprint (or cell footprint) and optimizes the control channel transmit power to minimize interference in other small cells. The focus is on that.

  Patent Document 2 describes a method in which a small cell adjusts the transmission power of its pilot based on a measurement report from a user equipment in order to reduce control signal interference.

  Patent Document 3 describes a method in which the small cell base station autonomously changes the transmission power of the control signal based on the strength of the received signal of the control signal from the macro base station and other small cell base stations. It is. The small cell base station obtains the path loss and the transmission power of other base stations based on the received signal. The type of the base station that transmitted the signal is classified, and the transmission power of the small cell base station is adjusted independently using information on the reception power from the macro base station.

  Patent Document 4 describes a method in which several fixed cells are formed around the same base station by a directional antenna and power control, and a target area is completely covered so that a blind spot does not occur. It is a thing.

  Patent Document 5 describes a method of adapting the transmission power of pilot signals of a plurality of base stations in order to adapt the coverage and satisfy the demands of users in the network.

  Non-Patent Documents 1 and 2 describe the concept of cell association used in a small cell network to reduce interference and increase capacity.

US Pat. No. 8,295,874 B2 European Patent Application Publication No. 2 071 738 A1 European Patent Application Publication No. 2 416 610 A2 European Patent Application Publication No. 2 068 577 A1 European Patent Application Publication No. 2 506 639 A1

Ye et al., “Capacity and Coverage Enhancement in Heterogeneous Networks,” IEEE Wireless Communications, 18 (3), June 2011 Andrews et al., “Femtocells: Past, Present and Future,” IEEE JSAC, 30 (3), April 2012

  It is an object of the present invention to provide a technique that improves interference control and resource allocation in a centralized small cell deployment so that it can cope with dynamic changes in user distribution and traffic requirements in the network.

  The object is achieved by a method according to claim 1, a computer system according to claim 12, an apparatus according to claim 13, a control plane base station according to claim 14, and a wireless communication system according to claim 15. Achieved.

According to the present invention, there is provided a method for constructing a virtual user plane cell including a certain user plane base station in a wireless communication system including a control plane base station having a coverage area including a plurality of user plane base stations. The This method
Identifying an anchor user from a set of users in the coverage area of the control plane base station;
Selecting a user plane base station capable of providing service to the anchor user from the plurality of user plane base stations within the coverage area of the control plane base station;
Associating, with the selected user plane base station, a mobile station that can receive service from the selected user plane base station of the set of users;
Constructing the virtual user plane cell including a selected user plane base station and a user associated with the selected user plane base station.

  According to an embodiment, the step of identifying the anchor user includes selecting a user satisfying one or more predetermined requirements from the set of users.

  According to the embodiment, the step of selecting the user plane base station is performed based on a network situation around each user plane base station in the coverage area of the control plane base station.

  According to an embodiment, the wide-area propagation state is obtained from a measurement report from a user or from a database having a wide-area propagation state around each of the user plane base stations in the coverage area of the control plane base station.

  According to an embodiment, the method may receive service from the plurality of users in the coverage area of the control plane base station from the user plane base station in the coverage area of the control plane base station. Determining the set of users by selecting a set of users.

  According to an embodiment, a user is identified from the set of mobile users according to one or more criteria of user capabilities, user mobility, user rate requirements, user contract class, and user transmission history. Selected. The user capability includes one or more of an operating frequency range, maximum transmission power, and transmission capability.

  According to an embodiment, building the virtual user plane cell includes assigning virtual cell identification information to the virtual user plane cell.

  According to the embodiment, the construction of the virtual user plane cell is performed by the control plane base station. The control plane base station sends information to the user plane base station through a backhaul link and sends information to the user by radio. The information sent to the user includes information about the virtual cell with which the user is associated and the user plane base station that provides the virtual cell. The information sent to the user plane base station includes information about the users associated with each virtual cell controlled by the user plane base station. The user plane base station exchanges data regarding the leaving user with a user plane base station that newly provides a service or through a control plane base station.

  According to an embodiment, the step of identifying, the step of selecting, the step of associating and the step of building are performed periodically.

  According to the embodiment, when resource reallocation is necessary due to the situation in the network, the time until the next execution is shortened. This situation includes one or more of user mobility, changing traffic requirements, macrocell load, user subscription situation, and user withdrawal situation.

  According to an embodiment, the method includes, for each constructed virtual small cell, the selected user plane base station, the associated user, the required capacity, and the maximum transmit power spectral density. Generating an enumerated table.

  The present invention provides a computer system that causes a computer to execute a method according to an embodiment of the present invention.

  According to the present invention, there is provided an apparatus for a wireless communication system comprising a control plane base station having a coverage area including a plurality of user plane base stations. The apparatus comprises a controller for constructing a virtual user plane cell including a user plane base station according to the method.

  According to the present invention, a control plane base station in a wireless communication system including a control plane base station is provided. The control plane base station has a coverage area including a plurality of user plane base stations. The control plane base station comprises a controller for constructing a virtual user plane cell including a user plane base station according to a method according to an embodiment of the present invention.

  According to the present invention, a wireless communication system is provided. The wireless communication system includes a control plane base station having a coverage area including a plurality of user plane base stations that provide services to one or more users. The system constructs a virtual user plane cell including user plane base stations according to a method according to an embodiment of the present invention.

  Embodiments of the present invention provide a novel approach for dynamically building a virtual small cell that is flexible enough to respond to dynamic changes in user distribution and traffic requirements within a wireless communication system. . An anchor user is selected to define a small cell footprint, a U-plane BS that can serve the anchor user is selected, and another service that may receive service from the selected U-plane BS. A user is also selected. A virtual small cell is defined by the selected U-plane BS and the user associated with it. According to embodiments of the present invention, even if the distribution of users or traffic requirements in the network change with time, resources can be efficiently allocated to meet the capacity requirements of the network. This approach only introduces a small overhead and eliminates the strict restrictions on the various backhaul connections that exist between macrocells and small cells, resulting in a flexible and low-cost network deployment. It is advantageous. A further advantage of embodiments of the present invention is the high capacity demands required of radio access networks, especially in the future deployment of such networks, in the architecture of overlay networks including macrocells and several small cells. The full potential of such networks can be realized in order to provide the potential to deal with and to meet the expected capacity requirements and to provide effective techniques for interference control and resource allocation. It will be like that.

  Embodiments provide integrated processing for interference control and resource allocation in a centralized small cell deployment. This process is flexible enough to respond to dynamic changes in the distribution of users and traffic requirements in the network. This process utilizes the concept of small cell construction and user association and uses specific criteria to select an anchor user that defines the footprint of the virtual small cell. In the process of associating users with dynamically constructed virtual small cells, transmission power requirements and capacity requirements are taken into account.

  According to a further embodiment, a simple centralized power control technique is provided for controlling the process of interference between virtual small cells so that the degree of resource reuse can be maximized.

  According to a further embodiment, the frequency division and assignment process is described. This process dynamically allocates enough frequency resources to meet the capacity requirements of another virtual small cell.

  In another embodiment, specific signaling and specific measurements are provided that will be performed by the user equipment and the small cell base station that enables the techniques of the present invention to be implemented.

  According to the above embodiment, even if the distribution of users or traffic requirements in the network change with time, it is possible to achieve efficient resource allocation to meet the capacity requirements of the network. At the same time, the embodiment only incurs minimal overhead, obviates the strict constraints on the type of backhaul connection that exists between macrocells and small cells, and as a result is very flexible and low Cost network can be deployed.

  Compared to the prior art summarized above, embodiments of the present invention focus on predetermining the maximum power that a small base station can use for transmission, ie, user equipment power control. In terms of focusing on power control by an independent base station, embodiments of the present invention provide a simple technique that allows control of transmit power for communication between a base station and a user terminal, and Is different.

  Change the transmission power level of the control signal based on the measurement received from the user terminal, for example by allowing cell to dynamically change its size by cell breathing. Compared to the approach, the embodiment of the present invention allows the central entity, i.e. the macro base station or the C-plane base station, to determine in advance the maximum size of the virtual cell. This size cannot be changed separately by a small cell base station.

  Compared with the technique described in Patent Document 1, according to the embodiment of the present invention, the macro base station sends a signal about the maximum transmission power that can be used for arbitrary communication to the small cell base station. Send explicitly. The small cell base station determines the transmission power to be actually used for data transmission within a range below the maximum value. Furthermore, the virtual small cell footprint is determined by the C-plane base station and not by conventional control signaling from the U-plane base station.

  Unlike U.S. Patent No. 6,057,059, embodiments of the present invention do not focus on pilot transmission. Rather, the maximum transmission power that can be used in the virtual small cell is set by signaling from the macro base station. The small cell base station independently selects actual transmission power within a preset range.

  Compared with Patent Literature 3, according to the embodiment of the present invention, the macro base station transmits a signal indicating only the maximum transmission power that the small cell base station is allowed to use for transmission to the small cell base station. Send. However, the macro base station does not explicitly or implicitly indicate the actual transmission power used by the small cell base station.

  Compared to US Pat. No. 6,057,089, embodiments of the present invention allow a virtual small cell to be dynamically formed to meet different capacity requirements, avoiding blind spots. It does not focus on. In addition, the concept of anchor user equipment is used to determine the footprint of the virtual small cell, which is in contrast to the teaching of determining the boundaries of the fixed cell being constructed.

  Compared to US Pat. No. 6,057,059, embodiments of the present invention do not focus on adapting the pilot signal transmission power, but rather the macro base station does not transmit pilot signals from small cell base stations. Determine the footprint of the virtual small cell.

  Unlike Non-Patent Documents 1 and 2, embodiments of the present invention teach the introduction of the concept of determining a virtual small cell service area using an anchor user equipment or user. .

  Thus, unlike the conventional approaches summarized above, embodiments of the present invention provide a centralized type for small cells based on information exchanged between small cells and macrocells using backhaul links. It offers the possibility to implement interference control and resource allocation. Embodiments of the present invention are advantageous because centralized interference control allows for efficient management of interference between small cells and associated improvements in system capacity.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

It is explanatory drawing which shows the whole structure of the network by which C plane and U plane were isolate | separated. FIG. 6 is an explanatory diagram illustrating a conventional technique that enables a small cell base station to adjust its own frequency to reduce interference and improve capacity. FIG. 2A shows the U plane at the first time point i. FIG. 2B shows the U plane at time j after time i. FIG. 6 is an explanatory diagram illustrating adjustment of power spectrum density and dynamic division of frequency resources of a small cell base station according to an embodiment of the present invention. FIG. 3A shows the U plane at the first time point i. FIG. 3B shows the U plane at time j after time i. It is explanatory drawing similar to FIG. 1 which shows the structure of the network by which C plane and U plane were isolate | separated. FIG. 3 is a flow diagram of a method for association and power allocation of a virtual small cell and a UE, according to one embodiment. FIG. 6 is an explanatory diagram showing inputs necessary for the virtual cell construction and association method of FIG. 5 and a method of giving them. It is explanatory drawing which showed an example of the construction | assembly of a virtual small cell and the correlation of UE and a virtual small cell using the method of FIG. A method for generating a virtual small cell and a method for associating each user, ie, each UE, with a respective small cell are shown. It is explanatory drawing which showed an example of the construction | assembly of a virtual small cell and the correlation of UE and a virtual small cell using the method of FIG. A method for generating a virtual small cell and a method for associating each user, ie, each UE, with a respective small cell are shown. It is explanatory drawing which showed an example of the construction | assembly of a virtual small cell and the correlation of UE and a virtual small cell using the method of FIG. A method for generating a virtual small cell and a method for associating each user, ie, each UE, with a respective small cell are shown. It is explanatory drawing which showed an example of the construction | assembly of a virtual small cell and the correlation of UE and a virtual small cell using the method of FIG. A method for generating a virtual small cell and a method for associating each user, that is, each UE, with a respective small cell are shown. It is explanatory drawing which showed an example of the construction | assembly of a virtual small cell and the correlation of UE and a virtual small cell using the method of FIG. A method for generating a virtual small cell and a method for associating each user, that is, each UE, with a respective small cell are shown. It is explanatory drawing which showed an example of the construction | assembly of a virtual small cell and the correlation of UE and a virtual small cell using the method of FIG. A method for generating a virtual small cell and a method for associating each user, ie, each UE, with a respective small cell are shown. It is explanatory drawing which shows the method of interference control and resource allocation of a virtual small cell by embodiment of this invention. FIG. 10 is an explanatory diagram showing a difference between fixed power allocation (FIG. 9A) and dynamic power allocation (FIG. 9B). It is explanatory drawing which shows the method of dynamic frequency allocation. FIG. 6 is an illustration of an embodiment that handles UE subscription. It is explanatory drawing of the method of handling the condition where UE leaves | separates. It is explanatory drawing of the radio | wireless communications system which has several macrocell. FIG. 4 is an explanatory diagram of the detached cell system of FIG. 3. The C plane BS 100 has a controller and a database. FIG. 4 is an illustration of an apparatus in the isolated cell system of FIG. 3 with a database and controller connected through an interface with a C-plane BS.

According to the embodiment of the present invention, a virtual user plane cell is constructed. More specifically, in a wireless communication system with a control plane base station having a coverage area including a plurality of user plane base stations, similar to that shown in FIG. The above virtual user plane cell is constructed. According to embodiments, an integrated resource allocation method is provided. In this method, a macro base station, eg, the C-plane BS of FIG. 1, dynamically constructs a virtual small cell using related information, associates a user equipment (UE) with the virtual small cell, and By adjusting the power spectrum density of the cell base station, the frequency resources are dynamically divided so as to meet the network capacity requirements. FIG. 3 is a view similar to FIG. That is, the user plane 108 has individual U cells 106 _{1 to} 106 ₄ , and each U cell has U plane BSs 104 _{1 to} 104 ₄ , respectively. A C plane BS 100 is also shown. Similar to FIG. 2, FIG. 3 also shows the user plane 108 at the first time point i (FIG. 3A) and the user plane 108 at the second time point j (FIG. 3B) thereafter. Yes. As shown in FIG. 3 (a) and FIG. 3 (b), according to the embodiment of the present invention, the power of each user plane base station is changed, and the allocation of resources (eg, frequency) is also changed. I understand that For example, regarding the U cell 106 ₁ , the power increases at a later time point j, and the frequency is divided so that a different frequency is used at the edge of the U cell 106 ₁ compared to the central area. Is done. In the same way, U cell 106 ₂ and U cell 106 ₃ is also changed. Furthermore, compared to the same cell at time i, as shown as a smaller U cell 106 _4, U cell 106 ₄ operates with less power.

  In the following embodiments, a method for forming a virtual cell according to an embodiment of the present invention will be described to address the shortcomings of the prior art methods referred to above.

FIG. 4 shows a network structure similar to FIG. 1 in which the C plane and the U plane are separated. In FIG. 4, the same reference numerals as those in FIG. 1 are used. In FIG. 4, in addition to the backhaul connections 110 _{1 to} 110 ₅ , according to an embodiment of the present invention, a backhaul link can be provided between one or more U-plane base stations. In the example shown in FIG. 4, the U-plane BS 104 ₂ U-cell 106 _2, the first U-plane backhaul link 118 ₁ is present between the U-plane BS 104 ₃ of U cell 106 _3. Another backhaul connection 118 ₂ between U-plane base stations 104 ₂ and 104 ₄ , between U-plane base stations 104 ₃ and 104 _4, and between U-plane base stations 104 ₄ and 104 _5. - 118 ₄ are present. Embodiments of the present invention provide a method of centralized resource allocation for small cells, which facilitates resource reuse and improves system capacity by C-plane BS 100 dynamically allocating virtual small cells. It applies the concept of the new cell association to be constructed and uses the power control of the U-plane BS to reduce the potential interference between virtual small cells.

According to another embodiment, a centralized dynamic frequency division algorithm is provided that can provide the U-plane BS 104 with sufficient resources to handle dynamic capacity demands in various parts of the network. The According to an embodiment of the present invention, the network deployment that results in the structure as shown in FIG. 4 comprises a macro base station or C-plane BS100. This base station controls a set of small cell base stations, ie U-plane BSs 104 _{1 to} 104 ₅ . As described above, the control plane and the user plane are separated from each other, and the macro base station is responsible for both the C-plane and U-plane communications, whereas the small cell BS is responsible for only the U-plane communications. To do. Necessary communication between the U plane base station and the C plane base station is performed through the backhaul 110 between the U plane 108 and the C plane 102, and a backhaul connection 118 is provided in the U plane. The backhaul connection 118 is also used.

  In the following embodiments relating to the construction of a virtual small cell, the association between the UE and the virtual small cell and the power allocation of the virtual small cell will be described. According to these embodiments, UE (user equipment) anchor and UE location, UE mobility, UE QoS requirements, UE measurement report, UE capability and U-plane BS capability information A virtual small cell is dynamically constructed based on the association between a macrocell-assisted UE and a virtual cell that can be performed on the basis thereof. Further, a centralized interference control method will be described. According to this method, each U-plane BS dynamically adjusts the maximum power spectral density that is allowed to be used in the frequency resources allocated to each U-plane BS.

  FIG. 5 is a flow diagram of a method for association and power allocation of a virtual small cell and a UE according to one embodiment. The method illustrated in FIG. 5 performs a combination of the construction of a virtual small cell, the association between the UE and the virtual small cell, and the power allocation of the virtual small cell.

  The method shown in FIG. 5 starts periodically or in response to a predetermined event, as indicated by reference numeral 200. In a first step 202, a set of UEs (user equipment, users or mobile users) is created. As shown at 204, a method according to an embodiment of the present invention receives a first input 204a that includes information about various inputs, eg, UE location, its mobility and its rate requirements. Further, information 204b including information on the position of the U-plane base station and its capability, and information 204c representing a large-scale propagation condition around each U-plane base station are included in the method. Given as input. In step 202 of creating a set of UEs, macro coverage of the C-plane base station 100 (see FIG. 4) or UEs in the coverage area 102 that will be served from the U-plane base station 104 in the coverage area 102. Determine a partial set of. The C-plane base station 100 uses the UE's mobility (for example, when a UE moving at high speed receives a service from the U-plane base station, such as an operating frequency range, maximum transmission power, and transmission capability). Will cause a large number of handovers), using criteria such as UE rate requirements, UE contract class, UE transmission history and further input parameters 204, etc. A partial set of UEs that may be served from the base station 104 is determined. The set of UEs is updated dynamically before each execution of the method and is updated dynamically at run time to remove the UEs associated with the virtual small cell. When the UE set is created in step 202, the method proceeds to step 206, and the anchor UE is identified from the UE set created in step 202. The anchor UE determines the footprint (or radio wave coverage) of the virtual small cell. Several criteria can be used to select an anchor UE from a set of UEs. For example, the anchor UE can be selected as the UE with the lowest rate requirement from the set of UEs. In this way, the virtual small cell boundary includes UEs with low rate requirements, making it easier to meet the QoS requirements at the edge of the virtual small cell. Alternatively, the anchor UE can be selected as the UE with the highest rate requirement to ensure that the high rate UE is offloaded as much as possible to the U-plane base station. According to another embodiment, the anchor UE can be selected as the most stable UE in terms of mobility, rate requirements or previous history, and the virtual small cell boundary remains stable over time Make sure. Note that in step 206, other criteria and weighted combinations of various criteria may be examined to select an anchor UE.

  After the anchor UE is determined from the set of UEs, the method proceeds to step 208 where the U-plane base station that has the best propagation state for the anchor UE is identified. The C-plane base station 100 can select a U-plane base station that gives the best SNR to the anchor UE using information obtained in advance about the wide-area propagation state around each U-plane base station 104. Other criteria can be used to narrow down the choices, for example, selecting a U-plane base station that meets the anchor UE requirements with the least power among all U-plane BSs 104 that meet the anchor UE requirements Can do. Wide area propagation using a measurement report from the UE (based on measurements of pilots of nearby U plane base stations) or from a database with wide propagation conditions around each U plane base station in the footprint of the C plane BS You can get the environment.

  If there are no U-plane base stations available to serve the anchor UE, the method proceeds to step 210 and it is determined that no suitable U-plane base station exists. In this case, the anchor UE selected in step 206 is associated with the C-plane base station 100, and is deleted from the UE set. Thereafter, the method returns to step 206 to identify a new anchor UE from the remaining UEs in the reduced UE set, and to identify a U-plane base station for the new anchor UE. Also made.

  If a U-plane base station is identified in step 208, the method proceeds to step 212 and after identifying the best U-plane base station for the anchor UE, the anchor UE is located around the U-plane base station. A virtual cell extending up to is constructed by the C-plane base station and assigned a specific ID, ie a virtual cell ID. The method then proceeds to step 214 where all UEs in the set of UEs that can be reliably serviced within that coverage area are associated with the virtual small cell constructed in step 212.

  The method then proceeds to step 216, where the identified user plane base station, virtual cell ID, UE, full rate requirement, and spectral power density assignment are indicated by the symbol 218, for example. And a virtual small cell association table. In this table, the anchor UE in the cell can be stored at the top of the list of related UEs. Further details for generating a table according to embodiments will be described later. The maximum power spectral density for each virtual cell is the minimum power spectrum required by the U plane BS in charge (specified U plane BS) to reliably serve the anchor UE in the virtual small cell. It can be determined as density. Several procedures can be used to determine the minimum power spectral density required to reliably serve the anchor UE, some of which will be described in more detail later. In step 216, the constructed virtual small cell, the associated UE, the serving U-plane BS for each virtual small cell, the required capacity for each virtual small cell, and the maximum transmission for each virtual cell. A table 218 listing the power spectral density is created.

  Thereafter, the method proceeds to step 219 where all stored UEs are deleted from the UE set. In step 220, it is determined whether there are any remaining UEs. If so, the method returns to step 206 and a new anchor UE for the new small cell is identified from the remaining UEs in the deleted UE set. Alternatively, if there are no UEs remaining, the method proceeds to frequency assignment process 222. This process will be described in more detail later.

  The method described with reference to FIG. 5 is performed in response to several inputs 204. The method of obtaining these inputs according to an embodiment of the present invention will be described in more detail with reference to FIG. FIG. 6 shows the inputs required for the virtual cell construction and association method of FIG. 5 and the methods by which those inputs are provided. More specifically, FIG. 6 illustrates the construction of a virtual small cell, the association of the UE with the virtual small cell, the power allocation of the virtual small cell, and the interference source, as will be described in more detail later. It shows how the input is processed at the C-plane base station 100 to obtain both a potential interferer table and an SNR table that can be used in the identification. The input 204 shown in FIG. 5 is shown on the left side of FIG. Inputs 204a regarding UE location and rate requirements are obtained from each UE. More specifically, as indicated by reference numeral 224, UE location and rate requirements are signaled from each UE to the C-plane base station 100. The input 204b, ie, the location and capability of the U-plane base station, is known at the C-plane base station 100, as shown at 226.

The input 204c, ie, the wide-area propagation state around each U-plane base station, can be obtained in various ways, for example by applying a channel sounding technique. FIG. 6 shows a further embodiment for obtaining a wide-area propagation state around each U-plane base station. In a first step 228, a set of quantized maximum transmit spectral power density levels T ₁ , T ₂ ,..., _TN are determined. These levels can be defined by the C-plane base station or specified in the communication standard used.

In a next step 230, each U-plane base station 204 transmits a pilot with a supported power level in a corresponding resource block (eg, frequency) allocated for this purpose. The resource block can be determined by the C-plane base station 100 or can be specified by a standard. Pilot transmissions are coordinated by the C-plane base station 100 to avoid excessive interference. In a next step 232, each user equipment UE measures the bandwidth of the pilot periodically or as needed and reports the following information:
-U-plane base station detected by transmission power level-Corresponding RSRP (reference signal received power) and SNR (signal to noise ratio)

This information is sent from each UE to the C-plane base station 100. The C-plane base station uses this information to generate an SNR table 236 and a potential interferer table 238 in step 234. The SNR table can be used for cell association and power allocation, with a maximum SNR for each defined maximum transmit spectrum power density level T _{1 to} T _{N and} for each user equipment UE _{1 to} UE _M. Each resulting U-plane base station detected at each level is shown. For example, the user equipment UE ₁ detects the user plane base station “1” (ID = “1”) having an SNR of 14 dB at the level T ₂ .

The potential interferer table 238 can be used to identify the interferer, each user at each level for each maximum transmit spectral power density level T ₁ -T _{N and} for each user equipment UE ₁ -UE _M. Fig. 4 illustrates user plane base stations detected by a device that exceed a certain threshold. For example, the user equipment UE ₁ detects user plane base stations “1” and “3” that are potential interference sources at level T ₂ .

  It should be noted that the above approach for obtaining wide-area propagation conditions around a U-plane base station is one possibility. More specifically, the use of pilot transmission at the quantized level is one way to obtain a wide-area propagation environment. Other techniques such as probing can also be used. The main point is that the SNR table and potential interferer table are generated based on the technique described above with reference to FIG. 6 or based on other techniques. Because these tables then select a base station in the user plane for the user equipment and as a basis for determining the frequency resources that will be allocated to the virtual cell based on potential interference sources. Because it plays a role.

  In other words, the C-plane base station 100 configures the above SNR table 236 and potential interference source table 238 using the measurement report from the UE. In the embodiment described with respect to FIG. 6, the maximum transmit power density for the virtual cell is the minimum power density that can be used by the controlling U-plane base station to achieve the rate requirements of the anchor UE in the virtual cell. Selected as. Based on the maximum power allocation for each virtual small cell, the C-plane base station constructs an interference graph using the potential interference source table.

Hereinafter, an example regarding the construction of a virtual small cell and the association between the UE and the virtual small cell using the method of FIG. 5 will be described with reference to FIG. FIGS. 7 (a) -7 (k) show how virtual small cells are created and how each user or UE is associated with a respective virtual small cell. . FIG. 7A shows the situation at the start. The user plane 108 includes user plane base stations BS1, BS2, and BS3. Assume that there are 11 UEs in the U plane 108. In FIG. 7A, the number on the upper left of the user equipment indicates the number of the UE, and the number on the lower right indicates the desired data rate for each user equipment. The lower part of the figure shows the table 218 described with reference to FIG. 5, which will be added when the algorithm of FIG. 5 is applied. FIG. 7 (a) shows an algorithm in which a set of UEs has already been created as described in step 202 of FIG. 5, starting at step 200 (see FIG. 5). In the example of FIG. 7, the set of UEs includes 11 UEs with each desired data rate associated therewith. In the next step, an anchor UE is identified from the set of UEs (see step 206 in FIG. 5). In the example of FIG. 7, the anchor UE is selected as the UE with the highest data rate requirement. As described above with reference to FIG. 5, other requirements may be considered, but the example described with reference to FIG. 7 assumes the highest rate requirement. In the set of UEs shown in FIG. 7 (a), the user equipment UE1 indicated by the dashed circle has the highest rate requirement, ie the highest desired data rate. Therefore, in step 206 of FIG. 5, UE1 is selected as the anchor UE. With respect to the anchor UE1, the U-plane base station BS1 is identified as the base station having the best propagation state for the anchor UE (see step 208 in FIG. 5). In this way, the anchor plane and the virtual small cell are determined by the user plane base station 1 and the user equipment UE1, and a virtual cell ID, for example, ID “a” is assigned to this cell (see step 212). . Thereafter, all UEs that can be covered with a relatively small spectral power density are associated with the U-plane BS1 (see step 214). In the example of FIG. 7, of all the UEs around the U-plane base station BS1, that is, UE2, UE3, UE4, only UE4 is identified as a UE that can be covered with a small spectral power density and is also a virtual small cell. As shown in FIG. 7B, which also shows “a”, it is associated with the U-plane base station BS1. As shown in FIG. 7 (c), in the table 218, the selected U-plane base station BS1 or ID “a” and the associated UEs or UE1 and UE4 are stored (step 216). reference). In this table, the anchor UE is initially saved so that the first entry in the associated UE column indicates the anchor UE. In this case, it is UE1. Furthermore, the total rate requirement for the associated UE is shown, which is 12 in the example shown in FIG. This is because the rate requirement of UE1 is 10, and the rate requirement of UE4 is 2. Further, the maximum transmission power T1 ^{, BS1} is also stored. After storing the information referred to above according to step 216, the method described with respect to FIG. 5 deletes the stored UE from the set of UEs in step 219, as shown in FIG. Only UE5 to UE11 remain. Since the set of UEs still includes the UE, the method returns to step 206. Among the UEs remaining in the UE set, the UE having the highest rate requirement is selected as the anchor UE.

The situation shown in FIG. 7 (d) shows two UE candidates that are highest and have the same rate requirement, namely UE5 and UE8. The UE 8 is selected as the anchor UE, and the U plane BS3 is specified as the U plane base station having the best propagation state for the anchor UE. The virtual small cell defined by the anchor UE8 and the U-plane BS3 has an associated virtual cell ID “b”. Of the remaining UEs, only UE 9 can be covered with a small spectral power density and is therefore determined to be associated with U-plane BS3. As shown in FIG. 7 (e), this information indicating the virtual cell ID “b” and associated UEs 8 and 9 having a total rate requirement of 9 is stored in the table 218 for the U-plane BS3. The The maximum transmission power ^{T8, BS3} is also shown. As can be further seen from FIG. 7 (e), the UE associated with the U-plane BS3 is deleted from the UE set, and UE2, UE3, UE5 to UE7, UE10, and UE11 remain.

The method proceeds to the next iteration, as shown in FIG. 7 (f), the UE 5 with the highest rate requirement is selected as the next anchor UE and the U-plane BS2 as the base station with the best propagation state for the UE 5 Is identified. The virtual small cell defined by the U-plane BS2 and the anchor UE5 has the ID “c”. Of the remaining UEs, only UE 6 can be covered with a small spectral power density, and is therefore determined to be a UE associated with U-plane BS2. As shown in FIG. 7 (g), this information is stored in a table 218, ie, U-plane BS2 is associated with virtual cell ID “c” and includes UEs 5 and 6 having 10 as the total rate requirement. It is shown. Also shown is the maximum transmission power T5 ^{, BS2} . Furthermore, the stored UE is deleted from the UE set, and only UE2, UE3, UE7, UE10, and UE11 remain.

  The method then proceeds to the next iteration step, and the UE 10 with the highest rate requirement among the remaining UEs is selected as the next anchor, as shown in FIG. 7 (h). For this anchor UE, the U-plane BS3 is determined as the base station having the best propagation state. The virtual small cell defined by the U-plane BS3 and UE10 has a cell ID “d”. Of the remaining UEs, only UE7 can be covered with a small spectral power density, and it is further determined that UE7 is also associated with U-plane BS3. As shown in FIG. 7 (i), the table 218 is updated accordingly. Then, the stored UE is deleted from the UE set, and only UE2, UE3, and UE11 remain in the UE set.

  As shown in FIG. 7 (j), among these remaining UEs, UE3 is selected as the next anchor UE, and it is determined that U-plane BS1 has the best propagation state for anchor UE3. The virtual cell defined by the U plane BS1 and the anchor UE3 has the ID “e”. Of the remaining UEs, only UE2 is determined to be a UE that can be covered by the U-plane BS1 with a small spectral power density. As shown in FIG. 7 (k), the table 218 is updated accordingly, the saved UE is deleted from the UE set, and only the UE 11 remains in the UE set. Thereafter, the system returns to step 206 and UE 11 is identified as the next anchor UE. However, since there is no appropriate U-plane BS that can be used by the UE 11, the UE 11 is associated with the C-plane base station 100 (see FIG. 3) as described with reference to FIG. 5 (see step 210).

  Thereafter, since it is determined that no UE remains in the UE set, the method of FIG. 5 ends. If, according to an embodiment, a frequency allocation approach as shown in step 222 of FIG. 5 is desired, the method can proceed to that frequency allocation.

  In the following description, embodiments of the present invention that enable frequency allocation of virtual small cells will be described in more detail. According to this embodiment, a two-stage method for virtual cell frequency allocation is provided. In the first stage, the interference source is identified in the dynamic interference environment brought about by dynamic power control, and in another stage, the frequency resources are dynamically divided to cause unnecessary interference. Allocate enough resources to meet various virtual small cell capacity requirements without wasting resources.

  FIG. 8 illustrates a virtual small cell interference control and resource allocation scheme according to an embodiment of the present invention. For the interference source identification step, the interference identification algorithm 300 is executed. This algorithm receives as input the UE and virtual small cell association table 218 generated by the method of FIG. 5 and the potential interferer table 238 described above with respect to FIG. Based on the inputs from these tables, the interference identification algorithm 300 outputs a virtual cell interference graph 302. The interference identification algorithm can be executed centrally by the C-plane BS 100 or distributedly by the U-plane BS 104 and aggregated at the C-plane base station 100 periodically or on demand. In the next step, a dynamic frequency resource partitioning and allocation algorithm 304 is performed that can be centrally performed by the C-plane BS 100 after identifying the interference sources. This algorithm 304 uses a virtual cell interference graph 302 generated by the interference identification algorithm 300 and a resource requirement 306 for each virtual cell derived from the full rate requirements shown in table 218 for frequency allocation. Receive as input. Thereafter, the algorithm 308 outputs a frequency allocation result 308 for each virtual cell.

Dynamic power allocation presents a new challenge in identifying interference because the environment of interference constantly changes as the transmission power of the U-plane BS changes. This will be described with reference to FIG. The figure shows the difference between fixed power allocation (FIG. 9 (a)) and dynamic power allocation (FIG. 9 (b)). The figure illustrates how dynamic power allocation provides a dynamic interference environment that makes it difficult to identify potential sources of interference. The upper part of FIG. 9 shows the situation at the first time point i, and the lower part shows the situation at the subsequent second time point j. It is assumed that the user equipment UE and three U planes BS1 to 3 are provided. In the situation of fixed power allocation shown in FIG. 9A, it is assumed that all U-plane BSs perform transmission at the maximum power T _max . Furthermore, as indicated by a solid arrow for the UE, the BS 1 transmits a desired signal, and the UE receives service from the BS 1. Due to the presence of BS2 and BS3, the UE also receives interference signals. Since the UE is closer to BE2 than BS3, the UE receives a strong interference signal (indicated by a dotted arrow) from BS2, and receives a weak interference signal from BS3 as indicated by a dashed arrow. In FIG. 9A, since the fixed power allocation is performed, the situation is the same at time point i and time point j. When dynamic power allocation as shown in FIG. 9B is performed, the situation changes. Assume that at the time point i, the base stations 1, 2 and 3 perform transmission at different power levels T _1a , T _2a and T _3a , respectively. In the example described with reference to FIG. 9B, the UE receives a service from the base station 1 and receives a desired signal as indicated by a solid arrow. The transmission power level of each of the base stations 2 and 3 is such that the transmission power of the base station 2 only generates a weak interference signal as indicated by the dashed arrow, and the transmission power T _3a of the base station 3 is It is assumed that no interference is observed. However, if the transmission power level is changed at time j, the interference situation may change as shown in the lower part of FIG. 9B. Although the transmission power T _1a of the base station 1 does not change, the transmission powers T _2b and T _3b of the base stations 2 and 3 increase. Thereby, unlike the time point i, the UE is assumed to receive a strong interference signal as indicated by a dotted line from both the base station 2 and the base station 3 at this time point.

  In order to cope with changes in the status of interference sources, an extensible approach for frequency control and power allocation and a reliable approach for identifying potential interference sources are required. Furthermore, this needs to facilitate the discovery of small cells even when the transmission power of the small cells changes. To address this problem, the C-plane base station needs to obtain a wide-area propagation environment around each U-plane base station, and several mechanisms for obtaining this information can be used. One example of accomplishing this is that a U-plane base station transmits a pilot for channel measurement. The UE measures the pilot and reports the channel condition to the C-plane base station. C-plane base stations can use this information to allocate power to each U-plane base station in an optimal manner to mitigate potential interference. Another approach is to obtain a wide-area propagation environment around each U-plane base station at the C-plane base station and use this information as input to maintain a database that constructs potential interference tables for various power allocations It involves doing. Embodiments of the present invention provide yet another approach that can be implemented for this purpose. According to this approach, the power level that can be used by the U-plane base station is limited to a fixed number. The U-plane base station transmits pilot symbols with a supported power level in a specific resource block allocated for this purpose, while the C-plane base station performs pilot transmission to reduce interference, Harmonize with the specific resources used for that pilot transmission. The UE measures specific resource blocks periodically or as needed and is detected beyond a given threshold at each power level and the maximum achievable SNR by the serving U-plane BS and at each power level. And information such as identification information of the U-plane base station that may be received. This information is either reported directly to the C-plane BS or collected at the U-plane BS and aggregated at the C-plane BS. The C-plane BS uses this information to construct the potential interference source table described above with respect to FIG. Along with the UE and virtual small cell association table 218 described with respect to FIG. 5, the C-plane BS obtains all the information necessary to construct an interference graph for all virtual cells for any power allocation.

  The dynamic frequency allocation technique uses the interference graph and the relative capacity requirements of the virtual cell so that all cell capacity requirements can be met fairly without causing interference. Dynamic resource partitioning. This technique is shown in FIG. In the first step, the capacity demands of all virtual small cells are normalized and the capacity demands are determined from a table 218 that shows all rate requirements for each virtual cell. Thereafter, as indicated by reference numeral 310, the vertex coloring algorithm of the interference graph of the virtual small cell is applied to obtain the number of colors. For each color, as shown at 312 in FIG. 10, the maximum relative capacity requirement of all virtual cells to which that color is assigned is determined, and depending on the maximum relative capacity requirement for each color, the frequency band (X MHz) is divided. After dynamic frequency division, the C-plane BS has several factors such as the capabilities of each U-plane BS, the capabilities of the UEs associated in the virtual small cell, and the history of previous assignments per U-plane BS. In consideration of the above, as shown by reference numeral 314 in FIG. 10, frequency resources are allocated to the U-plane BS that provides services to each virtual small cell.

In the following, embodiments of the present invention relating to discovery of assisted virtual small cells will be described. As described above, the C plane BS associates the UE with the virtual small cell. Therefore, the UE does not know in advance the virtual cell that needs to be connected. In order to facilitate the discovery of a virtual small cell, a macro cell-assisted virtual small cell discovery method will be described. According to this method, the C-plane BS sends relevant information over the backhaul link to the U-plane BS and over the air to the UE. The U-plane BS may provide buffer data for the UE to leave, such as if there is a direct link, directly with the U-plane BS that provides the service or between such U-plane BSs. If there is no hole link, it can be exchanged through the C-plane BS. According to the embodiment of the present invention, the C-plane BS sends the following information to each U-plane BS.
-Resource allocation for each virtual small cell under the control of the U-plane BS, including: o Frequency resources to be used o Maximum transmit power spectral density allowed for each frequency resource o Resources for transmitting pilot signals Block-UE associated with each virtual cell
-Destination of buffer data regarding UE to leave The following information is sent from the C-plane BS to each UE in the coverage area.
-A virtual small cell with which the UE is associated-a resource block for searching for a pilot signal-connection information about the associated virtual cell

  In the following, an embodiment for handling the problem of dynamic processing will be described. In order to get maximum benefit from the above approach to virtual small cell construction, UE to virtual small cell association and dynamic frequency allocation, several mechanisms have been implemented in the real world Deployment can be facilitated. This involves a technique for determining when to perform the above method and a technique for determining a method corresponding to the joining or leaving of the UE to the system after each execution of the method. Embodiments of the present invention include the method shown in FIG. 5 and further steps for dynamic frequency division and allocation. According to an embodiment, an integrated method for constructing virtual small cells, associating UEs with virtual small cells, virtual small cell power allocation and dynamic frequency division allocation is regularly implemented. Is executed automatically. The time until the next execution of the method is monitored using a resource allocation (RA) refresh counter. In order to perform the method periodically, a low time granularity, for example 5-10 minutes, is set. However, according to embodiments, a mechanism is provided that allows the method to be performed with higher time granularity when resource reallocation is required due to circumstances in the network. This is done by using external factors such as UE mobility, changing traffic requirements, macrocell load, etc. to decrease the RA counter faster than would occur in normal situations.

  Hereinafter, an example for explaining a method of handling the joining and leaving of the UE will be shown. After associating the UE with a virtual small cell, the network may move the UE, request a new UE to join the system, request to leave the existing UE's system, and request a new QoS request for the existing UE. Must handle etc. It is difficult to perform the above method whenever such an event occurs. On the other hand, when waiting until the next update time, there is a possibility that the service for some UEs may deteriorate. Therefore, according to the embodiment, two situations are specified in which the nature of the network can be changed and the examination of new resource allocation can be promoted. These situations are either UE subscription or UE departure.

  When a UE first requests access to the network, or for mobility or because of new QoS requirements that the serving virtual small cell cannot meet, the existing UE A subscription situation arises when it is necessary to connect to a small cell. On the other hand, for example, when an existing UE is moving out of coverage, the QoS requirements of that existing UE may no longer be met by the serving virtual small cell, Or, when an existing UE leaves the network (eg, when it is powered off or joins another macro cell), a leave situation occurs.

  FIG. 11 shows an embodiment for handling UE subscriptions. A subscription situation occurs when a new UE joins the network or when an existing UE moves out of the coverage of the associated virtual cell and enters the coverage area of another virtual cell. According to this embodiment, in a first step 400 it is determined for the target UE whether the UE becomes an anchor in the most feasible virtual cell. If this is not the case, at step 402 the UE will be associated with the most feasible virtual cell and the method ends at step 404. Otherwise, if the UE is an anchor in the most feasible virtual cell, the method proceeds to step 406, where the UE first serves the macro BS (eg, C-plane base station). Receive. In step 408, the macro BS decrements the RA refresh counter by an amount that can be weighted by the current macrocell load and the virtual small cell load. In step 410, it is determined whether the refresh counter update causes a new resource allocation. If so, the macro cell BS performs the cell association and RA algorithm described above (see step 412). Otherwise, the method ends. According to an embodiment, in the UE subscription situation, the most feasible virtual cell is the UE's desired among all virtual cells that have sufficient available capacity to meet the UE's desired QoS requirements. Can be defined as a virtual small cell that uses the lowest power spectral density to meet its QoS requirements. Another criterion can be used to define the most feasible virtual cell.

  FIG. 12 shows a method for handling the situation of leaving of the UE. A departure occurs when the UE leaves the network, leaves the coverage area of the associated virtual cell, or is turned off. In step 414, it is determined whether the UE is an anchor in a virtual cell that is providing service. If not, the method ends at step 416. This is because the situation does not substantially change due to the UE leaving, and as a result, resource allocation is not required. On the other hand, if the existing UE is an anchor of the virtual cell that is providing the service, in step 417, the macro base station sets the RA refresh counter, the current macro cell load, and the virtual small cell. Decrease by the amount weighted by the load. In step 418, it is determined whether the refresh counter update causes a new resource allocation. If so, the macro cell BS performs a cell association and RA algorithm in step 420. Otherwise, the method ends.

  In order to facilitate the method described with reference to FIGS. 11 and 12, each U-plane BS is controlled by each U-plane BS, including the size of the buffer, periodically or as needed. Information about the current load in each virtual cell is sent to the C-plane BS. This information can be used by the C-plane BS to determine the timing of each execution of the method and to minimize the possibility of handover.

  The above approach according to embodiments of the present invention is beneficial. This approach allows efficient load balancing and flexible small cell deployment without the need for detailed planning because frequency planning is done dynamically based on cell load and UE requirements This is because a high-performance backhaul capability is unnecessary. Additional benefits include increased resource reuse due to interference control, rapid response to changing user distribution and capacity requirements, and centralized small cell deployment with fixed power allocation is common. In particular, since the processing is performed at the maximum transmission power, the energy efficiency can be improved as compared with such a conventional method. Another advantage is that QoE (Quality of Experience) for the user can be further improved.

According to the embodiment, a wireless communication system including a plurality of macro cells 100 _{1 to} 100 ₄ each having a plurality of small cells is provided. That is, as shown in FIG. 13, this wireless communication system has a system of one or more separated cells as shown in FIG.

  According to the embodiment, the technique of the present invention can be implemented in the C-plane BS 100 including the controller 100a. The controller 100a controls the operation state of one or more U-plane BSs as described above. FIG. 14 shows a system of isolated cells similar to FIG. In this system, the C plane BS 100 also includes the controller 100a. Furthermore, according to the embodiment, the C-plane BS 100 also has a database 100b as shown in FIG. This database 100b stores the traffic value and the number of users for each grid element of a geographical grid element formed by dividing the coverage area 102 of the C-plane BS 100.

  According to a further embodiment, an apparatus can be provided. FIG. 15 shows the isolated cell system of FIG. 1 having a device 500 with a database 500a and a controller 500b. This device is connected to the C-plane BS 100 via the interface indicated by connection 502. The apparatus 500 stores each table described above in the database 500a, and provides each signal communicated with each U-plane BS through the interface 502 using a controller.

  Furthermore, according to the embodiment, the U plane BS 104 is provided with an interface for receiving a signal for controlling its own operation state as described above, for example, by its backhaul connection.

  Although some aspects of the described concepts have been described in the context of an apparatus, these aspects also represent descriptions of corresponding methods, where a block or device may correspond to a method step or a feature of a method step. it is obvious. Analogously, aspects described in the context of method steps also represent a description of the corresponding block or item or feature of the corresponding device.

  Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. Embodiments are implemented using a digital storage medium having electronically readable control signals stored thereon, such as a floppy disk, DVD, Blu-ray, CD, ROM, PROM, EPROM, EEPROM, or flash memory. They can (or can be) associated with a programmable computer system such that the respective method is performed. Thus, the digital storage medium can be computer readable.

  Some embodiments according to the present invention provide data having electronically readable control signals that can be coordinated with a programmable computer system to perform one of the methods described herein. Including a carrier.

  In general, embodiments of the present invention may be implemented as a computer program product having program code. The program code is operable to perform one of the methods when the computer program product is executed on a computer. The program code can for example be stored on a machine readable carrier.

  Other embodiments include a computer program that performs one of the methods described herein stored on a machine-readable carrier.

  Thus, in other words, one embodiment of the method of the present invention is a computer program having program code that performs one of the methods described herein when the computer program is executed on a computer. is there.

  Accordingly, a further embodiment of the method of the present invention is a data carrier (or digital storage medium or computer readable medium), the data carrier recorded on the data carrier as described herein. A computer program for executing one of the above.

  Thus, a further embodiment of the method of the present invention is a data stream or signal sequence representing a computer program that performs one of the methods described herein. The data stream or signal sequence can be configured to be sent over, for example, a data communication connection, eg, over the Internet.

  Further embodiments include processing means, such as a computer or programmable logic device, configured or adapted to perform one of the methods described herein.

  Further embodiments include a computer having a computer program installed that performs one of the methods described herein.

  In some embodiments, a programmable logic device (eg, a field programmable gate array) can be used to perform some or all of the functions of the methods described herein. In some embodiments, a field programmable gate array can work with a microprocessor to perform one of the methods described herein. In general, the method is preferably performed by any hardware device.

  The above-described embodiments are merely illustrative for the principles of the present invention. It will be understood that variations and modifications in the arrangements and details described herein will be apparent to those skilled in the art. Accordingly, it is intended that the invention be determined only by the appended claims and not limited to the specific details presented for the description and description of the embodiments herein.

Claims (15)

A virtual user plane cell including a user plane base station (104) in a wireless communication system including a control plane base station (100) having a coverage area (102) including a plurality of user plane base stations (104) Is a method of building
Identifying (206) an anchor user defining a footprint of a virtual small cell to be constructed from a set of users in the coverage area (102) of the control plane base station (100);
The user plane base station (104) having the best propagation state in providing services to the anchor user from the plurality of user plane base stations (104) in the coverage area (102) of the control plane base station (100) Selecting (208);
Associate users of the set of users that the selected user plane base station (104) can serve with a lower spectral power density than the anchor user to the selected user plane base station (104). Step (214);
Constructing the virtual user plane cell having a selected user plane base station (104) and a user associated with the selected user plane base station (104), comprising: A cell that extends to the anchor user about a selected user plane base station (104).   The method of claim 1, wherein identifying the anchor user includes selecting a user from the set of users that satisfies one or more predetermined requirements.   The step of selecting the user plane base station (104) is performed based on network conditions around each of the user plane base stations (104) in the coverage area (102) of the control plane base station (100). The method according to claim 1 or 2, wherein   A wide-area propagation state is obtained from a measurement report from a user or from a database having a wide-area propagation state around each of the user plane base stations (104) in the coverage area (102) of the control plane base station (100). 4. The method of claim 3, wherein:   Provision of services from a plurality of users in the coverage area (102) of the control plane base station (100) and from the user plane base station (104) in the coverage area (102) of the control plane base station (100). 5. A method as claimed in any one of the preceding claims, comprising determining the set of users by selecting a set of potential users. A user is selected from the set of users according to one or more of the following criteria: user capabilities, user mobility, user rate requirements, user contract class, and user transmission history;
6. The method of claim 5, wherein the user capabilities include one or more of an operating frequency range, a maximum transmission power, and a transmission capability.   7. The step of constructing the virtual user plane cell comprises the step (212) of assigning virtual cell identification information to the virtual user plane cell. Method. Construction of the virtual user plane cell is performed by the control plane base station (100),
The control plane base station (100) sends information to the user plane base station (104) through a backhaul link (110) and sends information to the user (112) by radio.
The information sent to the user includes information about the virtual cell with which the user is associated and the user plane base station (104) that provides the virtual cell;
The information sent to the user plane base station (104) includes information about users associated with each virtual cell controlled by the user plane base station (104);
The user plane base station (104) exchanges data regarding the leaving user with a newly serving user plane base station (104) directly or through the control plane base station (100). The method according to any one of claims 1 to 7, wherein   The method according to claim 1, wherein the identifying step, the selecting step, the associating step, and the constructing step are performed periodically. When reassignment of resources is necessary due to the situation in the network, the time until the next execution is shortened,
10. The method of claim 9, wherein the situation includes one or more of user mobility, changing traffic requirements, macro cell load, user subscription situation, and user departure situation. .   For each constructed virtual small cell, a table (218) listing the selected user plane base station (104), associated users, required capacity, and maximum transmit power spectral density. The method according to claim 9 or 10, comprising the step of generating (216).   A computer program product comprising a computer readable medium having computer readable instructions for causing a computer to perform the steps of the method according to claim 1. An apparatus for a wireless communication system comprising a control plane base station (100) having a coverage area (102) including a plurality of user plane base stations (104),
An apparatus comprising a controller (500b) for constructing a virtual user plane cell including a user plane base station (104) according to the method of any one of claims 1-11. A control plane base station (100) in a wireless communication system comprising a control plane base station (100),
A coverage area (102) including a plurality of user plane base stations (104);
A control plane base station (100) comprising a controller (100a) for constructing a virtual user plane cell including a user plane base station (104) according to the method according to any one of the preceding claims. A control plane base station (100) having a coverage area (102) including a plurality of user plane base stations (104) serving one or more users;
A wireless communication system for constructing a virtual user plane cell including a user plane base station (104) according to the method according to any one of the preceding claims.

Images